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Abstract:

Embodiments of the current invention include methods of forming a
strontium titanate (SrTiO3) film using atomic layer deposition
(ALD). More particularly, the method includes forming a plurality of
titanium oxide (TiO2) unit films using ALD and forming a plurality
of strontium oxide (SrO) unit films using ALD. The combined thickness of
the TiO2 and SrO unit films is less than approximately 5 angstroms.
The TiO2 and SrO units films are then annealed to form a strontium
titanate layer.

Claims:

1. An intermediate film for a capacitive device, comprising:a first
capacitive layer formed over a substrate;a plurality of SrO unit films
formed over the first capacitive layer;a plurality of TiO2 unit
films formed over the SrO film, wherein the ratio of the plurality of SrO
films to the plurality of TiO2 films is 3:4.

2. The film of claim 1, further comprising a second capacitive layer
formed over the plurality of TiO2 films.

3. The film of claim 2, wherein at least one of the first capacitive layer
and the second capacitive layer comprise an electrode having a material
selected from the group of titanium nitride (TiN), platinum, iridium,
iridium oxide, tungsten, tungsten oxide, molybdenum, molybdenum oxide,
ruthenium and ruthenium oxide.

4. The film of claim 1, wherein the plurality of SrO unit films comprise a
multiple of three monolayers.

5. The film of claim 1, wherein the plurality of TiO2 films comprises
a multiple of four monolayers.

[0002]Industry continues to search for new semiconductor materials that
exhibit a high dielectric constant and low leakage to enable further
miniaturization of electronic technologies. Such materials for example
may be used as the dielectric layer in electronic components such as
capacitors, memory cell structures, and other types of electronic
components. But, most materials investigated to date exhibit either high
dielectric constant and high leakage, or low dielectric constant and low
leakage. Therefore, industry has turned to investigating combinations of
these materials in order to develop materials with the requisite
properties. Strontium titanate (SrTiO3) is one such material that is
being investigated for having a high dielectric constant and low leakage.

BRIEF DESCRIPTION OF THE DRAWINGS

[0003]Various embodiments of the invention are disclosed in the following
detailed description and the accompanying drawings:

[0004]FIG. 1 is a flowchart describing a method of forming a capacitive
device including forming a strontium titanate film;

[0005]FIG. 2 is a flowchart describing a method of forming a strontium
titanate layer, according to one embodiment;

[0006]FIG. 3 is a flowchart describing a method of forming layers by
atomic layer deposition, according to one embodiment of the current
invention;

[0007]FIGS. 4A-4D illustrate the formation of a strontium titanate film by
atomic layer deposition;

[0008]FIG. 5 is a chart showing the results of a study of strontium
titanate film compositions having various ALD supercycle thicknesses and
ratios;

[0009]FIG. 6A is a graph showing the relationship between the ALD
supercycle thicknesses and the dielectric constant values in strontium
titanate films;

[0010]FIG. 6B is a comparison of x-ray crystallography data of strontium
titanate films having varied supercycle thicknesses but the same
composition;

[0015]FIG. 9 is a graph comparing the leakage density of strontium
titanate films (approx. 0.52 Sr/(Sr+Ti)) where strontium is deposited
first to strontium titanate films where titanium is deposited first; this
graph also compares strontium titanate films annealed at different
temperatures and for different times;

[0016]FIG. 10 is a chart comparing a strontium titanate film that was
deposited by a method where 50 strontium presaturation pulses were used
to a strontium titanate film that was deposited by a method where 100
strontium presaturation pulses were used.

DETAILED DESCRIPTION

[0017]A detailed description of one or more embodiments is provided below
along with accompanying figures. The detailed description is provided in
connection with such embodiments, but is not limited to any particular
example. The scope is limited only by the claims and numerous
alternatives, modifications, and equivalents are encompassed. Numerous
specific details are set forth in the following description in order to
provide a thorough understanding. These details are provided for the
purpose of example and the described techniques may be practiced
according to the claims without some or all of these specific details.
For the purpose of clarity, technical material that is known in the
technical fields related to the embodiments has not been described in
detail to avoid unnecessarily obscuring the description.

[0018]Embodiments of the current invention include methods of forming a
strontium titanate (SrTiO3) film using atomic layer deposition
(ALD). More particularly, the method includes forming a plurality of
strontium oxide (SrO) unit films using ALD and forming a plurality of
titanium oxide (TiO2) unit films using ALD. The combined thickness
of the SrO and TiO2 unit films is less than approximately 5
angstroms. The SrO and TiO2 units films are then annealed to form a
strontium titanate layer. This anneal may occur before the deposition of
any other material over the SrO and TiO2 unit films. The strontium
titanate layer formed by these methods and others described herein may
have an increased dielectric constant and an improved electrical leakage
value (J). In embodiments, the strontium titanate film may be the
dielectric layer of a capacitive device.

[0019]FIG. 1 illustrates a flowchart describing an embodiment of forming a
capacitive device that includes a strontium titanate dielectric film. At
block 101 of FIG. 1 a first conductive layer 405 is formed over a
substrate 403, as illustrated in FIG. 4. The first conductive layer 405
may be a material such as titanium nitride (TiN), platinum, iridium,
iridium oxide, tungsten, tungsten oxide, molybdenum, molybdenum oxide,
ruthenium and ruthenium oxide that are often used as the electrode
materials of dynamic random access memory (DRAM) cells.

[0020]In an embodiment, a strontium oxide (SrO) film 410 may then be
deposited over the first conductive layer 405 at block 102. In this
particular embodiment, SrO is deposited on the first conductive layer
before the deposition of titanium oxide because experimental data have
shown that depositing SrO first may lower the leakage density of the
ultimately formed strontium titanate film, as will be shown later in the
experimental results section. The SrO film 410 may be deposited by a
vapor deposition method such as atomic layer deposition (ALD) or chemical
vapor deposition (CVD). The flowchart of FIG. 2 describes forming a
plurality of SrO unit films using ALD or CVD. At block 201 of FIG. 2 a
plurality of SrO unit films are deposited using atomic layer deposition
(ALD) or CVD. The strontium oxide unit films are formed as described in
blocks 301 and 302 of the flowchart of FIG. 3 by forming at block 301 a
strontium-containing monolayer on a substrate by pulsing a strontium
precursor over a substrate and at block 302 by oxidizing said strontium
containing monolayer by pulsing an oxygen containing source over the
substrate. The oxygen containing source may be selected from the list
including ozone, oxygen, plasma activated oxygen, and water.

[0021]At block 301 a strontium (Sr)-containing monolayer is formed by
pulsing a Sr precursor over the substrate. In embodiments of the current
invention, the strontium-containing precursors may be polydentate
β-ketoiminates which are found, for example, in co-pending
application US20070248754A1, U.S. Ser. No. 11/945,678 filed on Nov. 27,
2007, co-pending application U.S. Ser. No. 12/266,806 which was filed on
Nov. 11, 2008, and co-pending application or U.S. Ser. No. 12/245,196
which was filed on Oct. 3, 2008. In certain embodiments, the polydentate
β-ketoiminates may incorporate an alkoxy group in the imino group.
The polydentate β-ketoiminates are selected from the group
represented by the following Structure A.

[0022]Structure A is defined as

##STR00001##

[0023]wherein M is Strontium; R1 is selected from the group
consisting of alkyl, fluoroalkyl, cycloaliphatic, having from 1 to 10
carbon atoms, preferably a group containing 1 to 6 carbon atoms, and an
aryl group having from 6 to 12 carbon atoms; R2 is selected from the
group consisting of hydrogen, alkyl, alkoxy, cycloaliphatic, having from
1 to 10 carbon atoms, preferably a group containing 1 to 6 carbon atoms,
and an aryl group having from 6 to 12 carbon atoms; R3 is selected
from the group consisting of alkyl, fluoroalkyl, cycloaliphatic, having
from 1 to 10 carbon atoms, preferably a group containing 1 to 6 carbon
atoms, and an aryl group having from 6 to 12 carbon atoms; R4 is a
C2-3 linear or branched alkylene bridge with or without chiral
carbon atom, thus making a five- or six-membered coordinating ring to the
metal center; R5-6 are individually selected from the group
consisting of alkyl, fluoroalkyl, cycloaliphatic, having from 1 to 10
carbon atoms, preferably a group containing 1 to 6 carbon atoms, and an
aryl group having from 6 to 12 carbon atoms, and they can be connected to
form a ring containing carbon, oxygen, or nitrogen atoms.

[0024]The temperature of the substrate during deposition of the strontium
precursor may be in the approximate range of 290° C. and
310° C., and more particularly approximately 300° C. This
temperature range is selected because it is the temperature window within
which the deposition of the strontium precursor is optimal. The
Sr-precursor can be delivered to the deposition chamber using vapor draw
(with or without charging up), bubbling, or direct liquid injection. A
carrier gas may be used to deliver the Sr-precursor. The choice of
delivery system typically depends on the particular ALD deposition tool.
The Sr-precursor is pulsed into the ALD reaction chamber for a time
sufficient to form a monolayer or less of the Sr-precursor material on
the substrate. The absorption of the precursor on the substrate is
self-limiting, so under ALD process mode conditions the absorption should
stop once the monolayer or less of the precursor material has formed on
the surface. In an embodiment, the pulse time for the Sr-precursor to
form one monolayer on the substrate may vary from tool to tool, precursor
delivery method, substrate temperature, and similar factors. For example,
the pulse time may be approximately one second on a Cambridge NanoTech
atomic layer deposition tool (Savannah) with 20 SCCM Argon carrier gas at
300° C. The pulsing of the Ti-precursor may be followed by a purge
by an inert gas such as Argon. In one particular embodiment, using the
Cambridge NanoTech ALD tool described above, the purge may be a five
second argon purge.

[0025]This class of strontium precursors have been found not to
incorporate detectable amounts of carbon in the films. Without being
bound by theory, it is postulated that with these precursors the Sr
ligand bonds are completely oxidized during exposure to an oxygen
containing source such as ozone or oxygen. The oxidation in the flow
occurs at block 302 of the flowchart of FIG. 3. At block 302 a strontium
oxide (SrO) unit film is formed by reacting the Sr-containing monolayer
with ozone as the oxidizer. The use of ozone is practical and
cost-effective because an exotic oxidizer is not needed. The forming of
the SrO film is then repeated to form multiple layers of the SrO film
during the ALD supercycle. An ALD supercycle is when more than one unit
film is layered to obtain a particular thickness of material. For
example, in FIG. 4A the multiple layers of the SrO unit films 411, 412,
413, 414, 415, and 416 may be in the form of a film stack 410.

[0026]In an embodiment, the deposition of the strontium monolayer may
include multiple pre-saturation pulses. The pre-saturation pulses may be
performed during only the first Sr-precursor deposition of SrO film 411
over the first conductive layer 405. The number of pre-saturation pulses
may be in the approximate range of 50-200 pulses in a Cambridge NanoTech
atomic layer deposition tool (Savannah). Experimental results of
embodiments of the current invention support this claim.

[0027]At block 103 of the flowchart in FIG. 1 a titanium oxide (TiO2)
film is also deposited over the conductive layer. The TiO2 may also
be deposited by the method described in the flowchart of FIG. 2 at block
202 by forming a plurality of TiO2 films using ALD. More
specifically, the ALD deposition may occur as described in FIG. 3 at
blocks 304 and 305. At block 304 a Ti-containing monolayer is formed on
the substrate by pulsing a Ti precursor over the substrate. The Ti
precursor may be chosen from the family of liquid group 4 precursors are
represented by the following formula I:

##STR00002##

In formula I above, M comprises Ti; R1 is an alkyl group comprising
from 1 to 10 carbon atoms; R2 is an alkyl group comprising from 1 to
10 carbon atoms; R3 is chosen from hydrogen or an alkyl group
comprising from 1 to 3 carbon atoms; R4 is an alkyl group comprising
from 1 to 6 carbon atoms.

[0028]In a particular embodiment, the titanium precursor (Ti-precursor)
may be described as Ti-1, a precursor in which the titanium atom is
coordinated with 2 tert-butoxy groups and 2 unsymmetrical beta-diketonato
resulting in a preferred coordination number of 6 for Ti atom. The
substrate may be a conductive layer such as an electrode described above
in relation to the SrO deposition or the substrate may be one or more
layers of the previously deposited SrO films. The temperature of the
substrate may be in the approximate range of 250° C. and
400° C., and more particularly in the approximate range of
290° C. and 310° C., and even more particularly
approximately 300° C. This temperature range is selected because
it is the temperature within which the deposition of this class titanium
precursor, and in particular Ti-1, is optimal. The Ti-precursor can be
delivered to the deposition chamber using vapor draw (with or without
charging up), bubbling, or direct liquid injection. A carrier gas may be
used to deliver the Ti-precursor. The choice of delivery system typically
depends on the particular ALD deposition tool. The Ti-precursor is pulsed
into the ALD reaction chamber for a time sufficient to form a monolayer
or less of the Ti-precursor material on the substrate. The absorption of
the precursor on the substrate is self-limiting, so under optimized
process conditions the absorption should stop once the monolayer or less
of the precursor material has formed on the surface. In an embodiment,
the pulse time for the Ti-precursor to form one monolayer on the
substrate may vary from tool to tool, precursor delivery method,
substrate temperature, and similar factors. For example, the pulse time
may be approximately one second on a Cambridge NanoTech atomic layer
deposition tool (Savannah) with 20 SCCM Argon carrier gas at 300°
C. The pulsing of the Ti-precursor may be followed by a purge of an inert
gas such as Argon. In one particular embodiment the purge may be a five
second argon purge on the Cambridge NanoTech ALD tool described above.

[0029]In an embodiment, there may be multiple pre-saturation pulses of the
Ti-1 precursor before the deposition of the first TiO2 unit film,
particularly in the instance where the Ti-1 precursor is deposited
directly on an electrode. This may have an effect on the formation of the
intermediate layer between the electrode and the TiO2 film which may
reduce the overall leakage of the strontium titanate film that is
ultimately formed. Experimental results of embodiments of the current
invention support this claim.

[0030]At block 305 of FIG. 3 a TiO2 unit film is formed by reacting
the titanium containing monolayer with ozone (O3) as the oxidizer.
In an embodiment, the temperature of the substrate is maintained at the
same temperature as the deposition of the Ti-precursor monolayer. Ozone
is pulsed into the ALD deposition chamber for a time sufficient to
oxidize all of the titanium atoms in the Ti-containing monolayer. As
described above for the formation of the Ti-precursor monolayer, the
oxidation reaction is self-limiting and therefore under the optimized
conditions will not continue reacting once all of the titanium precursor
molecules have been oxidized. In one particular embodiment, the ozone is
flowed into the deposition chamber for a pulse time of approximately 1
second followed an approximately 5 second argon purge. The Ti-1 precursor
and ozone may be selected to form the TiO2 film because they are
compatible and ozone is a practical and cost effective oxidizer.
Additionally, as will be in the Experimental Results section, the
combination of the Ti-1 precursor and ozone may also lower the carbon
content of the ultimately formed strontium titanate film.

[0031]Multiple TiO2 unit films are formed by repeating the forming of
the TiO2 film during an ALD supercycle at block 306 of the flowchart
in FIG. 3. An ALD supercycle is when more than one unit film is layered
to obtain a particular thickness of material. The plurality of TiO2
unit films is illustrated in FIG. 4A as the film stack 420 that is made
up of the individual TiO2 unit films 421, 422, 423, and 424. FIG. 4A
illustrates the TiO2 film stack 420 formed over the SrO film stack
410. The number of unit films depends on the ultimate ratio of titanium
to strontium desired in the final STO film. For purposes of example four
unit films of TiO2 are illustrated in FIG. 4A, but any number of
unit films may be deposited.

[0032]In this embodiment, the total thickness of the combination of ALD
supercycle to form the multiple depositions of the TiO2 unit films
illustrated as film stack 420 and the ALD supercycle to form multiple
depositions of the SrO unit films illustrated as film stack 410. The
total thickness of the SrO and TiO2 layers of unit films deposited
by the ALD supercycles has a thickness in the approximate range of 2
angstroms to 10 angstroms, and in some embodiments of less than
approximately 5 angstroms and in a more particular embodiment the total
thickness is in the approximate range of 3 angstroms and 4 angstroms. The
total thickness of both film stacks 410 and 420 of the SrO and TiO2
unit films was determined experimentally as those film stacks providing
improved dielectric constant and leakage data, as will be described in
more detail later.

[0033]Deposition of the plurality of SrO and the plurality of TiO2
unit films in multiple ALD supercycles may be repeated to ultimately form
a strontium titanate film having any predetermined thickness. FIG. 4B
illustrates one embodiment where only one SrO film stack and one
TiO2 film stack are formed, but this is not meant to be limiting.
Further ALD supercycle depositions may be performed above the TiO2
film stack 420, depositing SrO alternating with TiO2 to build any
predetermined thickness for the ultimate strontium titanate film. In an
embodiment, the predetermined thickness of the strontium titanate film
may be in the range of 10 nm-20 nm and more particularly approximately 15
nm. These thicknesses of the strontium titanate film were determined by
the optimization of the strontium titanate film to have a high dielectric
constant (k) of greater than 45 and more particularly a dielectric
constant of greater than 50 and may also provide lower leakage density
values, as will be shown in the Experimental Results. Additionally, in
one particular embodiment, the ratio of the plurality of SrO films in
film stack 410 to the plurality of TiO2 films in the film stack 420
for a capacitive device may be 3:2, or any multiple of the 3:2 ratio, for
example 6:4 (as illustrated in FIG. 4B) or 12:8. These ratios were
experimentally determined to provide lower leakage density as measured on
a completed strontium titanate film as will be shown in the Experimental
Results section. The flowcharts and figures describe a strontium titanate
film formed by first depositing SrO films before depositing TiO2
films. This embodiment is not meant to be limiting because in an
alternate embodiment a titanium oxide (TiO2) film may be deposited
first over the first conductive layer 405 followed by the deposition of
the SrO film.

[0034]At block 203 of the flowchart in FIG. 2, both the plurality of SrO
unit films (film stack 410) and the plurality of TiO2 unit films
(film stack 420) are annealed to form a strontium titanate (STO) layer
440 as illustrated in FIG. 4C. The annealing may be at a temperature in
the approximate range of 550° C. and 700° C., and more
particularly at a temperature of approximately 600° C. and
650° C. In one embodiment, represented by block 105 of FIG. 1, the
annealing of the SrO film stack 410 (or film stacks) and the TiO2
film stack 420 (or film stacks) may occur before forming a second
conductive layer over the STO film. Experimental results show that in
some embodiments annealing the SrO and TiO2 film stacks may provide
lower leakage density (J) and a higher dielectric constant (k) for
strontium titanate films formed by this method. In an alternate
embodiment, the annealing may occur after forming the second conductive
layer. The ambient atmosphere in which the annealing is performed may be
nitrogen gas, oxygen gas, or an inert gas. The composition of the
strontium titanate layer depends on the ratio of the number of TiO2
unit films to the number of SrO unit films deposited. During the ALD
supercycle described above and in blocks 101 and 102 of the flowchart of
FIG. 1, the forming of the TiO2 unit film is repeated a first number
of times and the forming of the SrO unit film is repeated a second number
of times, and the ratio of the first number to the second number is
selected to form a strontium titanate film having a predetermined
stoiciometry. In an embodiment of the current invention, the
predetermined stoiciometry may be in the approximate range of 0.48
Sr/(Sr+Ti) to 0.56 Sr/(Sr+Ti), and more particularly in the range of 0.50
Sr/(Sr+Ti) to 0.52 Sr/(Sr+Ti). In one particular embodiment, the
composition is formed to have a stoiciometry of approximately 0.52 atomic
% strontium in the strontium titanate film (Sr/(Sr+Ti)=0.52±0.2).

[0035]The selection of the Ti-1 and the Sr-precursor in combination with
ozone may lead to less incorporation of carbon in the final strontium
titanate film. It is theorized that the TiO2 unit film incorporates
little to no carbon because the Ti-precursor makes a clean break between
the Ti--C bonds during the reaction with ozone so that the oxygen from
the ozone may react only with the Ti atoms. It was unexpected that ozone
would be the best oxidizer for the formation of the TiO2 films using
the Ti-precursor. This is because ozone is often not compatible with many
Ti-precursors and, in embodiments of this invention, ozone is not only
compatible with Ti-1 but also ultimately provides low carbon strontium
titanate films. There may be no detectable carbon within bulk strontium
titanate films formed using ozone as the oxidizer, a strontium precursor
selected from the class of polydentate β-ketoiminates, and Ti-1
using the processing conditions described above. The ALD process is
optimized to form a strontium titanate film having no carbon in the bulk
portion of the film, where the detectable limit of carbon is an atomic
ratio of less than approximately 0.2. In one experiment a strontium
titanate film may be formed by the annealing of an ALD supercycle
nanolaminate where the number of titanium oxide layers is 10 and the
number of SrO layers is 20 (Ti:Sr=10:20). This forms a film having an
atomic percent of strontium of 0.60 (Sr/(Sr+Ti)) where there is no
detectable carbon in the bulk strontium titanate film and a small amount
of detectable carbon at the surface of the film. In another experiment, a
strontium titanate film may be formed by the annealing of an ALD
supercycle nanolaminate where the number of titanium oxide layers is 11
and the number of SrO layers is 20 (Ti:Sr=11:20). This forms a film
having an atomic percent of strontium of 0.57 (Sr/(Sr+Ti)) where there is
no detectable carbon in the bulk strontium titanate film and also no
detectable carbon at the surface of the film. Therefore, it has been
experimentally shown that a strontium titanate film formed by the
annealing of an ALD nanolaminate can be formed with an atomic percent of
carbon of 0.2 or less. The optimization of the strontium titanate film to
obtain a film having an atomic percent of carbon of 0.2 or less may be
accomplished through the selection of the precursors and the selection of
the process conditions. Minimizing the amount of carbon in the film
increases the dielectric constant of the strontium titanate film. Less
carbon is theorized to improve the crystallization of the strontium
titanate film into the cubic phase that maximizes the value of the
dielectric constant (k).

[0036]FIG. 5 shows a chart 500 having data of the predicted atomic percent
of strontium (column 501) vs. actual measured atomic percent of strontium
(column 502) for multiple strontium titanate films varied by the number
of TiO2 unit films (Ti cycles, column 503) and SrO unit films (Sr
cycles, column 504) deposited in an ALD supercycle. These experiments
were conducted to not only determine the actual stoiciometry of each
strontium titanate film, but also to provide strontium titanate films
from which physical and electrical data could be collected. As such, the
STO films represented by FIG. 5 were deposited on both SiO2 and
platinum (Pt) substrates. The Pt samples were used to identify the
optimal supercycle thickness and the optimal supercycle ratio of
TiO2 to SrO unit films within the supercycle to obtain a particular
atomic percent of strontium in the strontium titanate film. The study of
the strontium titanate films represented by the data in chart 500 of FIG.
5 compares different variations in the ratio of the number of TiO2
unit films to the number of SrO unit films within an ALD supercycle. In
the first set of experiments, set #1a in row 505, the composition of the
resulting strontium titanate film after annealing the film stack is the
same for each experiment, but the thicknesses of the individual unit
films within the ALD supercycle are varied. In the second set of
experiments, set #1b in row 506, the composition of the resulting
strontium titanate film is varied along with variation of the thicknesses
of the unit films within the ALD supercycle. The last two sets of
experiments, set #2 in row 507 and set #3 in row 508, represent extreme
variations of both the unit film thicknesses in a single ALD supercycle
as well as extreme variations in strontium titanate compositions.

[0037]FIG. 6A shows experimental data of the impact of the supercycle
thickness on the dielectric constant of the final strontium titanate
film. On the x-axis the supercycle thickness is plotted against the
dielectric constant (k) of the strontium titanate film. The optimal
thickness was found to be in the approximate range of 2 angstroms and 10
angstroms because the dielectric constant (k) values are the highest.
Obtaining a high k value while minimizing the thickness of the strontium
titanate film may be valuable in the use of strontium titanate films of
the current invention as the insulator in memory devices (such as DRAM.)
In FIG. 6A the impact of the ALD supercycle thickness on the dielectric
constant was studied. The ALD supercycle thickness is the combination of
both the TiO2 and SrO unit films. FIG. 6A plots the ALD supercycle
thickness in angstroms (Å) on the x-axis and the dielectric constant
(k) on the y-axis of the data from set #1a in row 505 of FIG. 5. The
graph shows that the highest dielectric constants (k) having values of
approximately 40 and higher are provided by ALD supercycle film stacks
having an ALD supercycle thickness of less than approximately 6
angstroms. These data suggest that an increase in ALD supercycle film
stack thickness may cause a decrease in dielectric constant of the
strontium titanate films. This graph also shows the difference in
dielectric constant values for strontium titanate films having
compositions of approximately 0.532 atomic percent strontium and
approximately 0.56 atomic percent strontium.

[0038]FIG. 6B shows that the variation in the ALD supercycle film stack
thickness does not impact the composition of the final resulting
strontium titanate films after annealing. FIG. 6B shows x-ray
crystallography data for strontium titanate films having the same ratios
of TiO2 unit films to SrO unit films but where the thicknesses of
those unit films was varied. The strontium titanate (110) peak position
did not change for any of the STO films analyzed. This result suggests
that the ALD supercycle thickness does not have a significant impact on
the final resulting composition of the STO films formed after annealing
the ALD supercycle film stack.

[0040]The variation of composition of the strontium titanate films may
have an impact on the dielectric constant (k) of the STO film. A sampling
of the strontium titanate films formed according to the data provided in
FIG. 5 suggest that higher amounts of strontium (Sr/(Sr+Ti)) in the
strontium titanate films increases the dielectric constant. The films
having a composition of approximately 0.50 Sr/((Sr+Ti) have the highest
dielectric constants of above approximately 40. More specifically, the
compositions of approximately 0.52±0.1 Sr/((Sr+Ti) yield a dielectric
constant (k) of above 50 and more particularly a k of 54.

[0041]FIG. 7A shows data of how the composition of the strontium titanate
film effects the leakage density (J) of the strontium titanate film.

[0042]FIG. 7B shows data of how the composition of the strontium titanate
film affects the effective oxide thickness (EOT) of the strontium
titanate film.

[0043]FIG. 8 provides another way to look at the optimal range of
supercycle film stack thicknesses and the optimal range of strontium
titanate compositions. The strontium titanate composition (Sr/(Sr+Ti)) is
plotted on the x-axis and the supercycle film stack thickness (angstroms)
is plotted on the y-axis to form a contour plot showing an area where the
dielectric constant values are optimized to be greater than 45.

[0044]FIG. 9: Leakage density was improved in this embodiment by
depositing SrO first.

[0045]FIG. 10: Prepulsing before first deposition on the first conductive
layer (electrode) improves leakage density of strontium titanate film.

[0046]Additionally, the ALD process is optimized to form a strontium
titanate film having no carbon in the bulk portion of the film, where the
detectable limit of carbon is an atomic ratio of less than approximately
0.2. FIGS. 7A and 7B show x-ray photoelectron spectroscopy (XPS) data of
the atomic percent of carbon in two strontium titanate films formed by
ALD using the Ti-AP-1 and Sr--C+precursors. FIG. 7A is an XPS analysis
graph of counts per second (CPS) (×103) vs. Binding Energy
(eV) of a strontium titanate film formed by the annealing of an ALD
supercycle nanolaminate where the number of titanium oxide layers is 10
and the number of SrO layers is 20 (Ti:Sr=10:20). For this film having an
atomic percent of strontium of 0.60 (Sr/(Sr+Ti)) there is no detectable
carbon in the bulk strontium titanate film and a small amount of
detectable carbon at the surface of the film. FIG. 7B is an XPS analysis
graph of CPS (×103) vs. Binding Energy (eV) of a strontium
titanate film formed by the annealing of an ALD supercycle nanolaminate
where the number of titanium oxide layers is 11 and the number of SrO
layers is 20 (Ti:Sr=11:20). For this film having an atomic percent of
strontium of 0.57 (Sr/(Sr+Ti)) there is no detectable carbon in the bulk
strontium titanate film and also no detectable carbon at the surface of
the film. Therefore, it has been experimentally shown that a strontium
titanate film formed by the annealing of an ALD nanolaminate can be
formed with an atomic percent of carbon of 0.2 or less. The optimization
of the strontium titanate film to obtain a film having an atomic percent
of carbon of 0.2 or less may be accomplished through the selection of the
precursors and the selection of the process conditions. Minimizing the
amount of carbon in the film increases the dielectric constant of the
strontium titanate film. Less carbon is theorized to improve the
crystallization of the strontium titanate film into the cubic phase that
maximizes the value of the dielectric constant (k).

[0047]Therefore, in an embodiment of the current invention based on
experimental results, an optimized strontium titanate film having a
dielectric constant value (k) of greater than 50 may be obtained using
methodologies disclosed herein. In one particular embodiment, a strontium
titanate film having a dielectric constant of greater than 50 may be
formed by the annealing of an ALD supercycle nanolaminate structure
having an overall thickness of approximately 15 nm. This ALD supercycle
nanolaminate structure is formed by repeating the deposition of a
plurality of TiO2 unit films and a plurality of SrO unit films where
the thickness of the TiO2 and SrO unit films in a single supercycle
are in the approximate range of 3 angstroms and 4 angstroms. Multiple ALD
supercycles may be performed to obtain the overall thickness of an
approximately 15 nm nanolaminate structure. The ratio of TiO2 to SrO
unit films within each of the ALD supercycles is selected to provide a
strontium titanate film having approximately 52 atomic percent strontium.
The combination of the supercycle thicknesses, the thickness of the ALD
supercycle nanolaminate structure, and the composition of the strontium
titanate film were experimentally determined, as shown by the results
described earlier, to provide an optimized strontium titanate film having
a k value of greater than 50.

[0048]Although the foregoing examples have been described in some detail
for purposes of clarity of understanding, the invention is not limited to
the details provided. There are many alternative ways of implementing the
invention. The disclosed examples are illustrative and not restrictive.